Heretofore, cationic polymers used as flocculants or paper chemicals are generally high molecular and water-soluble. Aqueous solutions of these cationic polymers exhibit a high viscosity even when they have a concentration as low as several percent and thus cannot be always handled easily during preparation, transportation and use. Therefore, various proposals have heretofore been made for the preparation process of cationic polymers and the form of these products. Among these proposals for the preparation process, the aqueous solution polymerization process is most commonly used as polymerization process. In this polymerization process, when the monomer concentration is raised to a value as high as scores of percent by weight for enhancing the production efficiency in an industrial mass production, the polymerization reaction solution exhibits an extremely high viscosity that causes gelation and thus can be hardly handled. In other polymerization processes such as suspension polymerization and emulsion polymerization, the handling and transportation of the resulting polymer solution are relatively easy. However, since these polymerization processes are effected with using a large amount of an organic solvent, the installation of a solvent recovery facility and the measure against dangers such as ignition add to the cost. Accordingly, it is considered most ideal to effect polymerization in an aqueous system in such a manner that the polymer solution can be easily handled from the whole standpoints of view.
Referring to the form of the product thus obtained, the product, if used as a flocculant for example, is often supplied in the form of a powder, which is dissolved in water before use. However, the powder form is disadvantageous in that it takes a lot of time to dissolve. In particular, it may involve the formation of coagulated portion, slightly soluble bulk material which makes fish-eye. This trouble may require a special dissolution facility. For example, it is required that the powder be added to water little by little through a feeder or the like. Besides the powder form, a W/O type emulsion has been recently put on the market. This type of a product normally has a low solution viscosity and thus can be easily handled. Further, this type of a product can be easily dissolved in water when used. However, an oil component such as high boiling hydrocarbon is generally used to disperse the emulsion and thus must be separated from water upon dissolution before use.
On the other hand, the above described polyvinylamine exerts an excellent effect in the application of cationic polymer as flocculant for waste water disposal, paper strength increasing agent, freeness improver or filler yield improver, and thus is expected to have a bright future. As a process for the preparation of such a polyvinylamine there has been known a process which comprises polymerizing an N-vinylformamide to obtain a poly-N-vinylformamide, and then modifying the poly-N-vinylformamide thus obtained under acidic or basic conditions so that the formyl group in the polymer is at least partially hydrolyzed, as described in JP-B-63-9523 (The term "JP-B" as used herein means an "examined Japanese patent publication"). Further, in order to further improve the various physical properties of the vinylamine, many copolymer polyvinylamines have been proposed, which are obtained by a process which comprises copolymerizing vinyl acetate, acrylonitrile, acrylic acid ester, etc. as a hydrophobic monomer with an N-vinylformamide or N-vinylacetamide as an N-vinylcarboxylic acid amide, and then modifying the copolymer thus obtained so that the formyl group or acetyl group is at least partially hydrolyzed, as described in JP-A-59-39399 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") JP-A-62-74902, JP-A-63-304, JP-A-63-10609 and JP-A-3-118804.
The above described polyvinylamines have been studied of their practical application in relatively recent years. These polyvinylamines exhibit a high dehydrating ability as compared with conventional cationic polymers having a quaternary ammonium group. Thus, these polyvinylamines are excellent in many respects as flocculant. However, there are no sufficient knowledge of its preparation process. Products other than those of powder type have almost never been reported.
The above described problems in the conventional process for the preparation of cationic water-soluble polymer and the product thus obtained arise also with respect to polyvinylamine. Thus, an efficient process for the preparation of polyvinylamine and a product which can be more easily handled as a flocculant or the like have been desired. Among N-vinylcarboxylic acid amide polymers are many polymers which are precipitated when obtained by polymerization in an aqueous medium and recovered as precipitates depending on the kinds and molecular weights of copolymerizing monomers. Such a water-insoluble polymer can hardly be kept in a stably dispersed state in the aqueous medium. Further, the polymer thus precipitated tends to be agglomerated. If this agglomeration is remarkable, the polymer solution can be insufficiently stirred, to thereby adversely affect the polymerization reaction. Further, the hydrolyzation reaction at the subsequent modification step cannot smoothly proceed. Moreover, polyvinylamines having satisfactory properties cannot be obtained.